1. Field of the Invention
The present invention relates to an electro-static discharge protection circuit to protect internal circuitry from electro-static discharge (ESD).
2. Description of the Related Art
An electro-static discharge protection circuit is established between an external source voltage supply line Vcc and internal circuitry of a semiconductor integrated circuit to protect the internal circuitry against a surge current caused by electro-static discharge (ESD) applied to the external source voltage supply line Vcc. As used herein, the term “internal circuitry” means one or more circuits to be protected against electro-static discharge (ESD) by an electro-static discharge protection circuit.
Electro-static discharge protection circuits using a rectifier with thyristors are known in the art, and one such circuit was disclosed in the 2004 EOS/ESD Symposium, “ESD Protection Solution for High Voltage Technologies”, (C. Principle of ESD-on-SCR). The electro-static discharge protection circuit includes a thyristor and a substrate resistance. The thyristor further includes a vertical PNP bipolar transistor and a lateral NPN bipolar transistor. Application of electro-static discharge (ESD) to the external source voltage supply line Vcc causes a current to be injected or charged into a chip capacitance. The current triggers the electro-static discharge protection circuit into an “ON” state of a thyristor mode. This electro-static discharge protection circuit is disclosed as “ESD-on-SCR (ESD-on-Silicon Controlled Rectifier)”. As used herein, the term “electro-static discharge protection circuit” means this type of circuit, that is, SCR.
When the external source voltage Vcc, for example 2.5 V, is applied to the external source voltage supply line Vcc, the booster circuit boosts the internal source voltage Vdd of the internal source voltage supply line Vdd up to 23.5 V. At the early stage of the boosting step, the external source voltage Vcc can be transiently greater than the internal source voltage supply line Vdd. At this early stage of the boosting step, a current which flows from the external source voltage supply line Vcc to the internal source voltage supply line Vdd can cause a thyristor included in a protection circuit to malfunction and turn on.
In view of the foregoing, an object of the present invention is to provide an electro-static discharge protection circuit which does not have the problems described above.
Another object of the present invention is to provide a semiconductor device with an electro-static discharge protection circuit which does not have the problems described above.